One type of such case involves the sudden, unexpected death of an infant or child. Sudden infant death syndrome (SIDS) is essentially a diagnosis that results from being unable to determine a specific cause of the sudden death of a child. The absence of gross pathological findings per se, however, is not a sufficient reason for a SIDS diagnosis; microscopic examination is essential to exclude other possible causes of death. Microscopic examination is particularly warranted when the child has a fatty liver, which may be due to Reye's Syndrome, enzymatic carnitine deficiency, acute alcoholic intoxication, sepsis, or undetermined causes. Another type of case that requires microscopic investigation is sudden, unexpected natural death in adults. Although as much as 55 percent of sudden, unexpected natural deaths in adults result from arteriosclerotic cardiovascular disease, microscopic examination is essential in addressing some key issues. These include the nature of the acute occlusion, whether an acute infarction occurred, the age of a recent occlusion or infarction, and whether the occlusion or infarction and death were precipitated or accelerated by external unnatural causes such as trauma and physical or mental stress. Microscopic examinations are also required when sudden, unexpected natural deaths of adults may involve a fatty change of the liver, embolism, myocarditis, diabetes, sickle cell disease, primary cardiomyopathies, conduction system lesions, and stress cardiomyopathy. Other types of cases that require microscopic findings involve gunshot wounds, a battered child, electrical and thermal burns, diffuse axonal injury, heat stroke, toxic injuries and poisoning, various environmental diseases, and abortion. Reasons why microscopic examinations are needed in such cases are discussed. 35 photographic exhibits and 77 references